In my copending application, Ser. No. 39,372, filed May 15, 1979, for "Microballistic Printer", I have shown a high-speed printer in which a plurality of solid projectiles are propelled in free flight across the space from a gun to the medium to be printed and in which the flight paths of the projectiles are so controlled as to produce impacts on the medium in the pattern of the desired printing. The projectiles are cycled in a path from a reservoir, to a gun, to the printing impact surface, then to a collector, from which they are returned to the reservoir.
It is undesirable to have projectiles, which have performed their function by striking a marking ribbon against a receiving medium such as paper on a platen, rebound and bounce around the walls of the collector and possibly strike a projectile on the way to the platen. This will destroy the desired pattern and create undesirable noise. Furthermore, by bouncing back and forth between the walls of the collector, the projectiles are delayed in their return to the reservoir, which will require a larger number of projectiles in the recycling stream.
If a projectile such as a ball drops on a surface which has a high coefficient of restitution, any material, including lead, will bounce from that surface. If the ball itself has a high coefficient of restitution and is dropped on a hard surface having a high coefficient of restitution, the ball will bounce to a very high degree; that is, it will lose very little energy. Stated otherwise, the rebound of a ball is a function of the coefficient of restitution of the materials of both the ball and the surface against which it strikes. If, however, the surface against which the projectile strikes is adapted to dissipate the energy by deforming or converting some of the energy into motion of a mass, the ball will not bounce. I have discovered that, if I take a thin sheet of material and support it by light foam, arranged either as a continuous layer or as discrete pillars or strips, the ball will not bounce from said surface when it strikes it. Apparently, I effectively transfer the kinetic energy from the ball to the thin sheet of resilient material, which deforms or dissipates the energy by flexing. The mechanism is not clearly understood, but a phenomenal result of no-bounce occurs. If I drop a ball on a surface slightly inclined from the horizontal, the ball strikes the surface, does not bounce, and rolls along the surface. If I make the angle horizontal, the ball strikes and stops dead. The ball or projectile may be approximately 0.8 millimeter or 32 mils in diameter and formed of steel. The sheet materials I have used were about one-tenth of a millimeter or four mils in thickness. Lesser thicknesses such as 0.05 millimeter or two mils may be used; however, the sheets of material are more fragile, more difficult to handle, and subject to crinkling. Greater thicknesses such as 0.2 millimeter or eight mils may be used; however, the tendency to rebound is somewhat increased. Sheets of 0.5 millimeter or 20 mils thickness are unsatisfactory for excessive rebound.